Lego Walkcycle Sliding Problem
So here is a method to make a non-sliding walk cycle. This is the Dopsheet part, once you have finished, when you'll move the character through the scene from point A to point B, you'll need to adjust the speed so that the walk doesn't slide, but it's another topic.


In the Dopesheet, put your cursor at frame 0, switch your armature to Pose mode, don't move the root bone for the moment, just create a pose with spread legs and hip a little bit down, align the heel of the front foot (let say left foot) with the tail of the root, select all the bones and create a LocRotScale keyframe.





Copy the whole pose, go to frame 20, paste the flipped pose, create a keyframe for all the bones. In the Dopesheet press T and choose Interpolation > Linear to make the Graph Editor curve linear.





Stay at frame 20, move the whole armature (with the bone) until the left foot is aligned with its position at frame 0 (which is now the position of right foot as the pose as been symmetrized). You can create an empty as a marker if it helps. Create a keyframe.





At frame 10 create the intermediary position: lift the right foot and move up the hip. Select all the bones and create a keyframe.





At frame 40, put the root bone at a position on Y axis that is twice its position at frame 20. Use the Location value in the N panel and keyframe it.





Now, copy the bones at frame 0 (except root) and paste them at frame 40. Insert a keyframe. Copy the bones at frame 10 poses (except root) and paste flipped at frame 30.





Disable the root animation so that the character walks but always stay at its position.